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Organic acids, as we employ the term here, are those acids that result from the synthetic activities of plants and animals, as distinct from decomposition acids, like uric acid, etc. For the purposes of this chapter, organic acids are those acids found naturally in fruits and vegetables, such as acetic, citric, malic, oxalic, etc., acids.
Carque says: "Organic acids are used by the living plants in their synthetic processes. In the ripening of some fruits some of the acids are progressively utilized in the formation of ethers and carbohydrates. Others are combined to form salts of potassium, sodium, calcium, magnesium, etc."
Organic acids in varying percentages exist in all fruits and vegetables. In many foods the acid exists in minute percentages, in none of them is the percentage of acid very great. They have a very pleasing flavor and are relished by everyone. A few of these, the most common ones, are as follow:
Citric acid, is found in oranges, lemons, limes, grapefruit, tangerines, qumquats, pineapples, pomegranates, tomatoes, citrons, quinces, gooseberries, raspberries, strawberries, currants, cranberries, and many others, either as an acid or else combined with alkaline salts forming citrates. Citric acid is absorbed from the digestive tract and, after being decomposed in the body, is eliminated by the kidneys as sodium carbonate.
Oxalic acid is perhaps the most widely distributed of all the organic acids, occurring in both fruits and vegetables. Cocoa, chocolate, coffee, and tea are particularly rich in it. So also are cranberries and rhubarb. The leaves of the rhubarb contain more than the stems. Tomatoes really have very little oxalic acid. Spinach contains many times as much oxalic acid as tomatoes. White bread, and even potatoes, contain much more of this acid than tomatoes. Sorrel is rich in oxalic acid.
Oxalic acid is most difficult for the animal body to oxidize and use. Opinions differ about its availability to the body. In excess it is probably productive of harm and is held responsible for some kidney stones. The percentage of this acid in most vegetables and fruits is so small that there is little danger of excess. A diet of spinach, tea, coffee and cocoa will easily introduce an excess into the body. In the normal person oxalic acid, whether entering the body as a free acid or as a salt, usually a calcium salt, undergoes oxidation into carbon dioxide and water, leaving its bases at the free disposal of the body.
Acetic acid is found in many plants. It combines readily with sodium, potassium, ammonium and other alkalies, forming salts or acetates, these acetates existing naturally in the juices of many vegetables. The acid and its salts are converted into alkaline carbonates in the body.
Malic acid is found in apples, apricots, cherries, cherimoyas, currants, loquats, mangos, papayas, pears, peaches, pineapples, plums, prunes, quinces, tomatoes, blackberries, cranberries, raspberries, strawberries, either in the free state, or in combination with alkaline bases, as malates, such as malate of calcium, malate of potash, malate of magnesium; and is found also in parsley, carrots and potatoes.
Tartaric acid is one of the most common organic acids. Grapes, mangos and tamarinds and other fruits contain this acid. As grapes ripen their tartaric acid disappears and sugar and other carbohydrates increase. The acids are apparently converted into sugars and starches.
Lactic acid is produced in the fermentation of milk sugar (lactose), when the milk sours. It exists in cheese and also in ripened cream. The fermentation of various sugars and starches and other substances, in the presence of protein, also gives rise to lactic acid as a by-product.
Nelson, of the Bureau of Chemistry found the acids of the strawberry are citric acid, 90%, malic acid 10%; pineapple acids, citric acid 87%; malic acid 13%; red raspberries acids, citric acid 97% and malic acid 3%; black raspberry acids, citric acid; concord grape acids, malic acid 60%, tartaric acid 40%.
Fruit acids and vegetable acids are beneficial only in their organic forms or as acid salts. The artificially prepared acids, sold in soft drinks and in other forms, never produce the beneficial effects that one obtains from the organic acids. Extracted acids are also not beneficial. Fruit and vegetable acids should be taken only in the fruit or vegetable in which they were formed or in the form of fruit juices and vegetable juices.
The older view that fruit acids produce acidosis, or that they increase blood acidity, still prevails in many quarters. This view is erroneous. Fruit acids actually do just the opposite of this--they increase blood alkalinity. Prunes, plums and cranberries are perhaps the only exceptions to the rule that acid fruits are all alkaline-ash foods.
Most of the various organic acids, such as citric and malic acids, are completely oxidized within the body. Benzoic acid contained in prunes, plums and cranberries is an exception. This is detoxicated by being converted into innocuous hippuric acid and eliminated in the urine. It has been found that more hippuric acid is eliminated than the limited amount of benzoic acid will account for. It is thought that the excess is derived from the quinic acid in these fruits.
Carque says: "The combined organic acids or salts consumed in food are generally changed in the body into alkaline carbonates, thereby increasing the alkalinity of the blood and secretions. The uncombined acids either form alkaline carbonates, or are oxidized into carbon dioxide and water."
The terminal product of the combustion, the acid radical of calcium salts of combustible organic acids, is carbonic acid and is excreted through the lungs and requires no bases to assist in its excretion. The entire calcium content of the salt remains at the free disposal of the body as a base. The same is true of the potassium, sodium and magnesium contained in the salts.
Blatherwick and Long found that drinking even large quantities of orange juice always results in producing an alkaline urine. They say: "It was impossible to over-reach the organism's ability to oxidize the contained citric acid," even though the. amount drunk was the equivalent of twenty-four large oranges eaten daily.
It is, nevertheless, true that in certain patients, after a considerable period on an acid-fruit diet, symptoms are produced that necessitate a change of diet. These patients become tense, restless, irritable, nervous and do not sleep well. The acid fruits begin to irritate them and they are uncomfortable after eating them. Such cases are relatively rare and are found almost wholly among thin, nervous patients. This would indicate that at least in some conditions of the body there is a limit to its power to oxidize organic acids. Like all other good things their use may be over done.
When organic acids are taken in excess of the body's abilities to effect their complete combustion into carbonic acid and water, they have the same effect as inorganic acids, as they have to be neutralized by being combined with bases before they can be eliminated.
The entrance of organic acids into the blood through other than the regular channels of digestion and absorption has proven fatal in experimental animals. In entering the body by the digestive tract, they enter the blood by first passing through the devious route of the lymphatic system, where they are at least partially changed and neutralized.
Berg mentions symptoms of acid poisoning arising out of the immoderate use of lemons (citric acid) in those undergoing the "lemon cure," popular in parts of Germany. Obviously, therefore, the body's power to utilize organic acids is limited and this power must vary with individuals and in the same individual, with the varying conditions of the body. The same fact must be true of these as inorganic acids--namely, that not until large doses of acids have been given for a considerable length of time, does the real "acidosis" result. A temporary excess, therefore, will result in no particular harm.
Most, if not all, of those cases where digestive troubles are occasioned by the use of acid fruits are due, not to the fruit or the acid per se, but to the combinations. Hundreds of patients have told me that they cannot eat fruits, that they cause indigestion, gas and discomfort. Almost invariably I have found that they were having oranges or grapefruit with a breakfast about as follows: Cereal with sugar and cream, egg on toast, coffee. Usually sugar was used on the grapefruit. When these patients are given an abundance of acid fruits, uncombined with other foods, they experience no discomfort or trouble.
Acid fruits are usually tabooed in gastric hyperacidity. As most cases of hyperacidity are not this at all, but are cases of acid fermentation in the excess of carbohydrates consumed, acid fruits taken with the meals, make the condition worse by their interference with salivary digestion. Taken when there is no other food in the stomach, they cause no trouble. A few cases of "sour stomach" (these may be cases of real hyperacidity) have their distress increased by the use of acid fruits, whether taken alone or in combination with other foods. A short fast usually enables these few to take the acid fruits. Acid fruits do not always aggravate gastric ulcer but should not be employed until the ulcer is healed. A fast best accomplishes this result.